The analysis of keratinized structures, particularly hair, for the identification and quantitation of ingested analytes is a well established practice (U.S. Pat. No. 5,364,642, U.S. Pat. No. 8,084,215). An important concern for hair analyte analysis is the change in hair condition induced by cosmetic treatment (e.g., bleaching, highlights, coloring or perms), heat treatment (e.g. heat of dryers, curling irons or flat irons) or other sources such as combing, humidity, dryness, dirt, sunrays (UV and infared radiation) and pollution in the atmosphere. However, hair damage occurs mostly in the form of physical and chemical changes as a result of bleaching, oxidative dyeing, hair relaxing via alkaline relaxers, reducing waving and curling preparation. In addition to the cosmetic treatments named above, hair can also exhibit damage from mechanical actions such as excessive brushing, rubber-banding (e.g., ponytails), [12] or constant friction (e.g. body hair against clothing). While chemical interactions between the cosmetic agents and the analytes themselves are one aspect of such cosmetic treatments, an effect common to all is damage to the hair, especially disruption of the cuticular sheath resulting in increased porosity of the hair.
Increased porosity of the hair affects two main aspects of hair analysis: (1) contaminants entering the hair and (2) compounds present from ingestion being lost from the hair. Regarding the first aspect, contaminants such as drugs diffuse into the hair as solutes in solvents, particularly hair-swelling solvents; water, which swells normal intact hair about 14-16% within 30 minutes is the most prevalent and likely solvent involved in real-life contamination. Porous hair can absorb 10-20 times as much drug as intact hair under the same exposure conditions. The second aspect of the effects of porosity in hair analysis, the loss of drugs from ingestion due to cosmetic damage, is very much a function of the degree of porosity caused by the cosmetic damage. If the porosity is extremely severe, which can result from applying cosmetic treatments in degrees not recommended by the cosmetic industry, drug may be lost from the sample even before the sample reaches the laboratory. Thus, there is a need to identify such samples as too damaged to produce a reliable result as to drug ingestion and reported accordingly.
The assessment of hair damage as a result of the aforementioned variables is desired to provide reproducible and reliable methods for determining the presence of targeted analytes in hair samples. Hair damage has been previously measured by a variety of methods including microfluorometry, colorimetric staining, microscopy, scanning electron microscopy and Wilhelmy wettability. These methods, while effective, suffer from their time-consuming and laborious nature. For example, hair damage can be determined by Methylene Blue staining (For Sci Int 176 (2008) 23-33), but the method requires staining and slide mounting of many individual samples, making it incompatible with high volume hair analyte analysis. Thus, a need exists for more rapid, high-throughput protocols that are amenable to the screening of high quantities of hair samples commonly found in hair analysis laboratories.